The present invention relates to a manufacturing method for a throttle body defining therein an air passage of an internal combustion engine (hereinafter, referred to as engine).
From recent requirements of weight reduction as well as cost reduction, there is known a throttle body whose housing is made of a resin. However, the throttle body is generally configured into a complicated shape with protrusions and recesses for providing bearing members of a throttle shaft and for installing an opening degree sensor.
More specifically, the housing of the throttle body supports both ends of the throttle shaft via the bearing members. The housing has two recesses formed for receiving the bearing members (at portions where the throttle shaft is supported). When the housing including these two recesses (hereinafter, referred to as retaining portions) is formed by resin molding, it is typical that two separate molding dies are prepared for forming these retaining portions.
However, when separate molding dies are used to form the two retaining portions, it is necessary to accurately adjust axial centers of these molding dies. Otherwise, axial centers of the bearing members resulting through the resin molding operation will not agree with each other. For example, even if the throttle shaft can be inserted into the bearing portions, disagreement of the axial centers of the bearing members will undesirably increase a rotational torque of the throttle shaft. This will generate an excessive drive loss when the throttle shaft is driven. Furthermore, requiring high accuracy in the setting of the separate molding dies will increase the manufacturing cost.
Furthermore, even if setting of the separate molding dies is accurately done, the axial centers of the bearing members may disagree with each other due to product tolerance of the bearing members themselves.
Unexamined Japanese patent publication No. 11-173227 proposes a manufacturing method for a throttle body. According to this method, a housing of the throttle body is formed by a composite material with a matrix of synthetic resin. Retaining portions of a throttle shaft are formed independent of the housing. The retaining portions are connected to a cylindrical portion of the housing by welding or the like so that deformation of the intake passage can be prevented.
According to this manufacturing method, the above-described molding dies are not used for forming the retaining portions of the throttle shaft. However, this conventional technique will encounter similar problems. For example, the separately formed retaining portions may not be accurately connected to the cylindrical portion of the housing. In this case, the axial centers of the bearing members disagree with each other. Furthermore, even if connection of the retaining portions with the cylindrical portion of the housing is accurately done, the axial centers of the bearing members may disagree with each other due to the tolerances of respective bearing members.
Furthermore, the above-described conventional technique requires a step of forming the retaining portions of the throttle shaft independent of the cylindrical portion of the housing and a step of connecting the retaining portions to the cylindrical portion. Thus, the total number of required manufacturing steps increases and the manufacturing cost increases.
Furthermore, the present invention relates to a throttle apparatus adjusting an intake air amount of the engine.
According to a conventional throttle apparatus, a disklike valve member is rotatably provided to adjust an intake air amount flowing in an intake passage. There is a throttle body whose main body is made of a resin for the purpose of reducing the weight of the throttle apparatus. The above-discussed unexamined Japanese patent publication 11-173227 discloses the throttle apparatus having a resinous or resin-made throttle body and bearing portions of a throttle shaft. The bearing portions are made of a resin material different from that of the throttle body and connected by welding to the throttle body.
However, the above-described conventional throttle apparatus requires the throttle body and two bearing portions which are separately formed. Thus, a total number of the parts increases. Furthermore, the above-described conventional throttle apparatus requires a step of connecting the bearing portions to the throttle body by welding or the like. Thus, the total number of manufacturing steps increases and the manufacturing cost increases.
In view of the foregoing problems of the prior art, a primary object of the present invention is to provide a resinous or resin-made throttle body for an engine throttle apparatus which is free from disagreement of axial centers of bearing members supporting both ends of a throttle shaft.
To accomplish the above and other related objects, the present invention provides a manufacturing method for an engine throttle body comprising a step of inserting a correcting shaft member into bearing members which rotatably support a throttle shaft fixing a valve member controlling an opening degree of an air passage, a step of placing the bearing members with the correcting shaft member inserted therein in a molding space of a molding die and integrally molding by a resin material a cylindrical portion of the throttle body defining the air passage and retaining portions supporting the bearing members, a step of, after finishing the molding step of the throttle body, extracting the correcting shaft member from the bearing members, a step of inserting the throttle shaft into the bearing members, and a step of fixing the valve member to the throttle shaft.
With this arrangement, it becomes possible to support the throttle shaft by the bearing members whose axial centers accurately agree with each other.
Furthermore, integrally forming the cylindrical portion and the retaining portions makes it possible to eliminate a step of connecting the cylindrical portion with the separately formed retaining portions. Thus, it becomes possible to facilitate the manufacturing process and reduce the manufacturing cost.
According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the bearing member is constituted by an anti-friction bearing. This enhances the effect of preventing the valve member from freezing due to icing phenomenon or from sticking due to accumulation of deposition, compared with a case where both of the bearing members are constituted by the sleeve bearing. Furthermore, in the molding step of the throttle body, an axial end of the anti-friction bearing is covered by a covering member. Thus, it becomes possible to conceal the rotational portion of the bearing against the resin material so as to assure smooth rotation of the bearing.
According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the covering member comprises a cylindrical wall covering a cylindrical side surface of the bearing. Thus, it becomes possible to conceal the rotational portion of the bearing against the resin material so as to assure smooth rotation of the bearing. Furthermore, a locking means is provided on the cylindrical wall for preventing rotation of the bearing. Thus it becomes possible to prevent the bearing from rotating in the resin during the molding operation. Thus, the bearing does not shift in the shaft thrust direction.
According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the throttle shaft has a smaller outer diameter at a portion accommodated in the cylindrical portion and a larger outer diameter at other portions accommodated in the retaining portions. Thus, it becomes possible to eliminate frictional contact between the throttle shaft and the cylindrical portion. The throttle shaft smoothly rotates without causing frictional loss. Accordingly, the opening degree of the valve member can be controlled properly. Adjustment of air flow amount in the air passage can be performed adequately.
According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the correcting shaft member is extracted in a predetermined direction in the extracting step of the correcting shaft member. Thus, the axial opposed end of the retaining portion can be closed. The rotational portion of the throttle shaft or the like is not exposed to the outside of the throttle body. Accordingly, it becomes possible to enhance the airtightness and fluid-tightness of the bearing member. No special plug or the like is required. Therefore, it becomes possible to simplify the arrangement, reduce the total number of parts constituting the throttle body, and reduce the manufacturing cost.
Moreover, in view of the foregoing problems of the prior art, the present invention has an object to provide a throttle apparatus capable of reducing the total number of parts and also capable of reducing the weight.
To accomplish the above and other related objects, the present invention provides a throttle apparatus having a throttle body made by a resin. At least one axial end of a throttle shaft is directly supported by the throttle body. This makes it possible to reduce the number of the bearing members which need to be separately produced for supporting the throttle shaft. The weight of the throttle apparatus reduces compared with a case where the throttle shaft is supported by a complicated bearing such as anti-friction bearing. Furthermore, the bearing structure for the throttle shaft becomes simple. The total number of parts reduces. Accordingly, the assembling of the throttle apparatus becomes easy and the manufacturing cost decreases.
Preferably, both axial ends of the throttle shaft are directly supported by the throttle body. This arrangement makes it possible to omit all of the bearing members which need to be separately produced for supporting the throttle shaft. Accordingly, the weight of the throttle apparatus reduces and the total number of parts reduces. Furthermore, the assembling of the throttle apparatus becomes easy and the manufacturing cost decreases.
Preferably, a coating is applied to the throttle shaft at the axial end region directly supported by the throttle body. This makes it possible to reduce frictional resistance between the throttle body and the throttle shaft.